This invention relates generally to the field of optical devices for laser generating systems, and more particularly to improvements in high energy laser mirror structures including a heat exchanger comprising means to circulate fluid coolant through the mirror structure.
Laser mirrors employed in the high power density environment of a high energy laser system must, for optimum performance, be configured to be structurally stable against the thermal stresses imposed on the mirror during laser operation.
Conventional high energy laser mirrors generally have a structure comprising a thin faceplate supporting the laser mirror reflective surface, and a supporting substructure including a heat exchanger defining internal fluid coolant flow channels. Two general types of distortions of the mirror surface may arise using conventional mirror structure configurations, namely, (1) pressure-caused distortions arising from pressurized fluid coolant flow within the heat exchanger, and, (2) thermally induced distortions resulting from stresses imposed on the mirror structure by laser heating. Further, thermally induced distortions may include beinding or warping of the mirror surface because of uneven heating of the mirror surface or of thermal gradients normally existing across the thickness of the faceplate. Further, thermal distortions may result from linear growth (thermal expansion) of the mirror structure and particularly of the heat exchanger (HEX) substructure, often referred to as "HEX growth". For optimum performance of the high energy laser mirror, surface distortions or other surface deformations of the mirror's reflective contour across the surface area thereof most affected by the impinging laser beam must be maintained at a minimum, and preferably at a fraction of the wavelength of the incident laser radiation.
The invention described herein provides an improved laser mirror, particularly useful in a high energy laser environment, having a novel heat exchanger substructure for conducting coolant fluid through the mirror structure. The novel heat exchanger structure of the present invention is uniquely configured generally in a isogrid-type configuration, which exhibits high thermal conductivity, structural strength and rigidity, and which is characterized by its light weight and high resistance to thermally induced distortions. The mirror structure described herein may be configured to utilize the isogrid structure to define a plurality of fluid inlet and outlet passageways for conducting coolant near the mirror surface, and, further, may be configured to provide metered zonal cooling to the mirror surface, in order to substantially reduce the thermal effects on the mirror structure resulting from energy density variations across the profile of the impinging laser beam.
It is, therefore, an object of the present invention to provide an improved high energy laser mirror structure.
It is a further object of the present invention to provide a lightweight high energy laser mirror structure wherein thermally induced mirror surface distortion is substantially eliminated.
It is yet another object of the present invention to provide a high energy laser mirror-heat exchanger structure providing metered zonal cooling to the mirror surface.
These and other objects of the present invention will become apparent as the detailed description of a representative embodiment thereof proceeds.